javascript problem under xslt

[LCH]

hi all~
I'm new to xslt, and I'm sorry about my poor English
I try to design a xslt that can auto change css file when day by day

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:lxslt="http://xml.apache.org/xslt"
xmlns:xalan="http://xml.apache.org/xalan"
xmlns:user="http://pc"
extension-element-prefixes="user"
>

<xalan:component prefix="user" functions="output">
<xalan:script lang="javascript">
function output(){
var today = new Date();
return today.getDay();
}
</xalan:script>
</xalan:component>


I use <xsl:value-of select="user:output()" /> try to use the value in the function , then I get a error the user dont hava any functions

Thanks in advance for any help.